Hydrogen storage systems using non-pyrophoric hydrogen storage alloys

ABSTRACT

A hydrogen storage system includes a hydrogen storage alloy containment vessel comprising an external pressure containment vessel and a thermally conductive compartmentalization network disposed within the pressure containment vessel. The compartmentalization network creates compartments within the pressure vessel within which a hydrogen storage alloy is disposed. The compartmentalization network includes a plurality of thermally conductive elongate tubes positioned within the pressure vessel forming a coherent, tightly packed tube bundle providing a thermally conductive network between the hydrogen storage alloy and the pressure vessel. The hydrogen storage alloy is a non-pyrophoric AB2-type Laves phase hydrogen storage alloy having: an A-site to B-site elemental ratio of not more than 0.5; and an alloy composition including (in at %): Zr: 2.0-5.5, Ti: 27-31.3, V: 8.3-9.9, Cr: 20.6-30.5, Mn: 25.4-33.0, Fe: 1.0-5.9, Al: 0.1-0.4, and/or Ni: 0.0-4.0.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to: U.S. Provisional Application Ser.No. 63/225,366 filed Jul. 23, 2021 entitled “Non-Pyrophoric HydrogenStorage Alloys and Hydrogen Storage Systems Using the Alloys”; U.S.Provisional Application Ser. No. 63/225,389 filed Jul. 23, 2021 entitled“Hydrogen Storage Systems Using Non-Pyrophoric Hydrogen Storage Alloys”;and U.S. Provisional Application Ser. No. 63/225,399 filed Jul. 23, 2021entitled “3D Printed Hydrogen Storage Systems Using Non-PyrophoricHydrogen Storage Alloys”. The entire contents of the foregoingapplications are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to hydrogen storage systemsusing non-pyrophoric AB₂-type Laves phase hydrogen storage alloy.

STATEMENT OF FEDERALLY FUNDED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

Hydrogen, generally considered to be the ultimate fuel, presentsnumerous potential benefits to be realized as well as numerousdifficulties to be overcome. With capacity to serve as a fuel forcombustion engines, other processes in which heat energy is derived fromcombustion and used; as well as a direct source of electrochemicalenergy in direct conversion processes such as, for example, those usedin electrochemical fuel cells, hydrogen presents opportunities forproduction of energy without the creation of waste products bearingdisposal difficulties.

The products of hydrogen combustion, whether thermal or electrochemical,are energy and water. Neither of these is toxic, neither presentsdifficulties of disposal of greenhouse gases, soot, or radioactivewaste. From the standpoint of being a useful, high-energy content fuel,hydrogen is an excellent candidate for most of the uses in which fossilfuels are currently used. When used for direct conversion to electricalenergy in a fuel cell, hydrogen does not yield oxides of carbon whichoften poison catalytic material used in such electrochemical cells, noris radioactive waste generated as is the case with electricity-supplyingnuclear-powered generators.

With these tremendous benefits accruing to its use as a fuel, someburdens in the use of hydrogen as a fuel may be expected. They arepresent and provide challenges to overcome. The greatest difficultieswith hydrogen as a fuel lie in its containment and transportation.Hydrogen may be liquefied but there is tremendous cost involved incooling and compressing; additionally, the containment vessel cannot becompletely sealed; tremendous losses are incurred through evaporation.Compression of the gas itself is costly, although not nearly so much asliquefaction, and requires stout, durable, and heavy containers. Bothare inefficient forms of storage in terms of energy storage per unitvolume. Other storage means would be useful.

Various metals and metal alloy compositions are available for storage ofhydrogen within the metallic crystal lattice, generally as a hydride.Metal hydride systems have the advantage of storing hydrogen at highdensity for long periods of time because they are formed by insertinghydrogen atoms into the crystal lattice of the metal. Storage ofhydrogen as a solid is appealing as enhanced volumetric efficiency isavailable. Such materials will generally release heat upon charging,take-up of hydrogen, absorption of hydrogen, or hydriding. Conversely,heat is necessary to release stored hydrogen from the metallicstructure.

Reversible metal hydrides are a broad class of materials that undergo areversible reaction with hydrogen. Overall reversible reaction iswritten as:M(s)+x/2H₂(g)⇔MHx(s)+ΔH  (1)where M is the hydridable alloy, MHx is the metal hydride and ΔH is theheat of formation of the metal hydride. The hydridable alloy surfacesserving to catalyze the breakup of hydrogen molecules into hydrogenatoms will be helpful prior to this reaction. The absorption reaction isexothermic, whereas the desorption reaction is endothermic. During thisreaction, the metal lattice expands with the absorption of hydrogen, andthe metal structure shrinks with the desorption of hydrogen, so thehydrogen storage alloy will usually have a larger effective surface areaor smaller particles. When they are exposed to air, there is anotherpossible reaction of these alloys:M(s)+x/2O₂(g)⇔MOx+ΔH  (2)

The metal powder has a huge heat-generating reaction with oxygen,causing the surface temperature to rise significantly. High temperaturecauses the instability of the surface oxide layer, leading to a chainreaction between the metal powder and oxygen. This is known aspyrophoricity.

This spontaneous combustion means that the material must be speciallyhandled by continuously providing a non-oxidativeatmosphere/environment. From the perspective of distribution andimprovement of hydrogen storage capacity, more importantly, thespontaneous combustion properties of these materials require specialtreatment during transportation. Their transportation methods are alsoseverely restricted; usually, for example, due to their pyrophoricnature, such materials cannot usually be transported by air. Therefore,the pyrophoric nature of certain hydrogen storage alloys is one of themain safety issues related to the commercial use of hydrogen storage inthe form of hydride alloys.

A series of non-pyrophoric metal hydrides are disclosed in U.S. Pat.Nos. 6,517,970 and 6,737,194 to Ovshinsky, et al., entitled“Non-pyrophoric hydrogen storage alloy”. The patents state that theOvshinsky alloys:

-   -   Generally the alloy comprises titanium, zirconium, vanadium,        chromium, and manganese. The alloy may preferably further        comprise iron and aluminum and may also contain 1-10 at % total        of at least one element selected from the group consisting of        Ba, Co, Cu, Cs, K, Li, Mm, Mo, Na, Nb, Ni, Rb, Ta, Tl, and W        (where Mm is mischmetal). Specifically the low temperature        hydrogen storage alloy comprises 0.5-10 at % Zr, 29-35 at % Ti,        10-15 at % V, 13-20 at % Cr, 32-38 at % Mn, 1.5-3.0 at % Fe, and        0.05-0.5 at % Al.

Unfortunately, compared with traditional metal hydrides, these prior artnon-pyrophoric materials have a pressure composition temperature (PCT)curve with a relatively high slope and greater hydrogen trapping. Thistrapping reduces the reversible storage capacity of the alloys andcreates various difficulties in practical application. New advancedmaterials with non-pyrophoricity, as well as high reversible capacity,low PCT curve slope (flattened plateau pressure), tailored plateaupressures and low material cost, are desired to meet the requirement ofpresent-day hydrogen storage systems.

The ideal hydrogen storage material for large-scale commercial use musthave:

-   -   1) a high storage capacity relative to the weight of the storage        alloy material;    -   2) suitable desorption temperatures/pressures;    -   3) good kinetics;    -   4) good reversibility,    -   5) the ability to resist poisoning (i.e. contamination of the        alloy by external impurities while cycling), including the        typical pollutants present in commercial hydrogen used for        cycling (e.g. oxygen and water vapor, commercial hydrogen is        only 99.995% pure); and    -   6) a relatively low cost.

If the material is missing any of these characteristics, it will beunfeasible for large-scale commercial use.

In many applications, especially when the hydride is used in mobileapplications, the hydrogen storage capacity per unit weight of materialis an important consideration. Relative to the weight of the material,the low hydrogen storage capacity can, for instance, reduce the mileageand therefore the driving range of hydrogen fuel vehicles using thismaterial. To reduce the energy required to release hydrogen, a lowdesorption temperature/high plateau pressure is required. Also, toeffectively utilize the available waste heat from vehicles, machinery,fuel cells or other similar equipment, a relatively low desorptiontemperature is required to release stored hydrogen.

Therefore, there is a need in the art for hydrogen storage materialsthat are non-pyrophoric, have a high reversible hydrogen storagecapacity, a low hydrogen desorption temperature/high plateau pressure, arelatively flat PCT isotherm curve plateau pressure, a low hysteresis,low trapping, and low materials cost.

SUMMARY OF THE INVENTION

The present invention comprises a hydrogen storage system. The hydrogenstorage system may include a hydrogen storage alloy containment vessel.The hydrogen storage alloy containment vessel may include an externalpressure containment vessel. The hydrogen storage alloy containmentvessel may also include a thermally conductive compartmentalizationnetwork disposed within the external pressure containment vessel. Thethermally conductive compartmentalization network may createcompartments within the external pressure containment vessel withinwhich a hydrogen storage alloy may be disposed. The thermally conductivecompartmentalization network may include a plurality of elongate tubesbeing made of a thermally conductive metal or alloy selected from thegroup consisting of aluminum, magnesium, copper and alloys of thesemetals. The elongate tubes may be positioned within the externalpressure containment vessel with longitudinal axes of the elongate tubesbeing parallel to a longitudinal axis of the external pressurecontainment vessel. The plurality of elongate tubes may form a coherent,tightly packed tube bundle within the external pressure containmentvessel such that the coherent, tightly packed bundle provides athermally conductive network between the hydrogen storage alloy and theexternal pressure containment vessel.

The hydrogen storage alloy containment vessel may further include ahydrogen storage alloy disposed therein. The hydrogen storage alloy maybe a non-pyrophoric AB₂-type Laves phase hydrogen storage alloy. Thealloy may have an A-site to B-site elemental ratio of not more thanabout 0.5. The alloy may have an alloy composition including about (inat %): Zr: 2.0-5.5, Ti: 27-31.3, V: 8.3-9.9, Cr: 20.6-30.5, Mn:25.4-33.0, Fe: 1.0-5.9, and Al: 0.1-0.4. More preferably, the alloy mayhave an alloy composition including about (in at %): Zr: 2.9-5.5, Ti:27-30.3, V: 8.3-9.3, Cr: 20.6-26.5, Mn: 29.4-32.1, Fe: 1.5-5.9, and Al:0.1-0.4.

The non-pyrophoric AB₂-type Laves phase hydrogen storage alloy mayfurther include up to about 4 at % nickel as an equal substitute for upto about 2 at % chromium or up to about 2 at % manganese or both. Thealloy may have a total hydrogen storage capacity of at least about 1.7wt % or 1.8 wt % at about 500 psi and about 20° C. The alloy may furtherhave a trapped hydrogen capacity of not more than about 0.25 wt %(preferably not more than about 0.2 wt % and more preferably not morethan about 0.15 wt % or 0.10 wt %) at about 14.5 psi and about 20° C.

The hydrogen storage alloy may have a PCT isotherm slope of no more thanabout 0.8 (preferably not more than about 0.7 or 0.6). Thenon-pyrophoric AB₂-type Laves phase hydrogen storage alloy may have ahysteresis of not more than about 0.5 or 0.4 (preferably not more thanabout 0.3 and more preferably not more than about 0.2 or 0.1).

The alloy may also contain about 1-10 at % total of at least one elementselected from the group consisting of Ba, Co, Cu, Cs, K, Li, Mm, Mo, Na,Nb, Ni, Rb, Ta, Tl, and W (where Mm is mischmetal).

An outer diameter of all tubes of the plurality of elongate tubes may bethe same. Alternatively, the outer diameter of each tube of theplurality of elongate tubes may be variable. At least some tubes of theplurality of elongate tubes may have one or more notches provided inlongitudinal sides thereof to provide access openings to an interior ofthe tubes.

Some tubes of the plurality of elongate tubes may have non-cylindricalcross-sections and some tubes may have corrugated interior and/orexterior wall surfaces.

A pressure valve may be connected to a valve opening of the externalpressure containment vessel.

The external pressure containment vessel and the thermally conductivecompartmentalization network disposed within said external pressurecontainment vessel may be formed simultaneously via 3D metal printing,such as 3D printing of aluminum and/or aluminum alloys. The 3D metalprinting may comprise deposition by Selective Laser Melting (SLM) and/orDirect Metal Laser Sintering (DMLS).

In addition, the present invention comprises a method of fabricating thehydrogen storage system by fabricating the external pressure containmentvessel and the thermally conductive compartmentalization networkdisposed within said external pressure containment vessel via 3D metalprinting, and depositing the hydrogen storage alloy within said hydrogenstorage alloy containment vessel.

The external pressure containment vessel and the thermally conductivecompartmentalization network disposed within the external pressurecontainment vessel may be formed simultaneously via the 3D metalprinting, such as 3D printing of aluminum and/or aluminum alloys. The 3Dmetal printing may comprise deposition by Selective Laser Melting (SLM)and/or Direct Metal Laser Sintering (DMLS).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent invention, reference is now made to the detailed description ofthe invention along with the accompanying figures and in which:

FIG. 1 displays desorption pressure composition temperature (PCT)isotherm plots for examples of the inventive non-pyrophoric hydrogenstorage alloys at 20° C.;

FIG. 2 displays the absorption and desorption (PCT) isotherm plots of aninventive non-pyrophoric hydrogen storage alloy vs. two comparablepyrophoric alloys at 20° C.;

FIG. 3 displays desorption PCT isotherm plots exhibiting the effects ofzirconium contents on the plateau pressures of the inventivenon-pyrophoric hydrogen storage alloys at 20° C.;

FIG. 4 displays desorption PCT isotherm plots (at 20° C.) of an A-sitelean non-pyrophoric hydrogen storage alloy of the present invention vs.an A-site rich non-pyrophoric hydrogen storage alloy of the prior artOvshinsky patents;

FIG. 5 displays desorption PCT isotherm plots for examples of theinventive non-pyrophoric hydrogen storage alloys with low iron contentsat 20° C.;

FIG. 6 depicts a hydrogen storage system according to the presentinvention;

FIG. 7 depicts a magnified image of the top of the hydrogen storagesystem in FIG. 6 ;

FIG. 8A depicts a cross-sectional view of a hydrogen storage systemaccording to the present invention showing internal tubes having outerdiameters that are all the same;

FIG. 8B depicts a cross-sectional view of a hydrogen storage systemaccording to the present invention showing internal tubes having variedouter diameters; and

FIGS. 9A-9D depict additional tubing varieties useful for the hydrogenstorage system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a non-pyrophoric, AB₂-type Laves phase hydrogenstorage alloy and hydrogen storage systems using the alloys. The alloymay preferably have an A-site to B-site elemental ratio of about <=0.5.The alloy may preferably have a total hydrogen storage capacity of atleast about 1.7 wt % or 1.8% wt % at about 500 psi and about 20° C. Thealloy may further have a trapped hydrogen capacity of not more thanabout 0.25 wt % (preferably not more than about 0.2 wt % and morepreferably not more than about 0.15 wt % or 0.1 wt %) at about 14.5 psiand about 20° C.

The hydrogen storage alloy may have a pressure composition temperature(PCT) isotherm slope of no more than about 0.8 (preferably not more thanabout 0.7 or 0.6). The non-pyrophoric AB₂-type Laves phase hydrogenstorage alloy may have a hysteresis of not more than about 0.5 or 0.4(preferably not more than about 0.3 and more preferably not more thanabout 0.2 or 0.1).

Broadly, the inventive hydrogen storage alloy contains about (in at %):Zr: 2.0-5.5, Ti: 27-31.3, V: 8.3-9.9, Cr: 20.6-30.5, Mn: 25.4-33.0, Fe:1.0-5.9, and Al: 0.1-0.4.

More narrowly, the inventive hydrogen storage may contain about (in at%): Zr: 2.9-5.5, Ti: 27-30.3, V: 8.3-9.3, Cr: 20.6-26.5, Mn: 26.4-32.1,Fe: 1.5-5.9, and Al: 0.1-0.4.

The alloy may also contain about 1-10 at % total of at least one elementselected from the group consisting of Ba, Co, Cu, Cs, K, Li, Mm, Mo, Na,Nb, Ni, Rb, Ta, Tl, and W (where Mm is mischmetal). Lowelectronegativity elements (such Ba, Cs, K, Li, Na, Rb, Mm) can purifythe alloy by reacting with impurity oxides, while relatively highelectronegativity elements (such as Co, Cu, Mo, Nb, Ta, Tl and W) can bedissolved in AB₂-type Laves phase to improve hydriding properties.

The non-pyrophoric AB₂-type Laves phase hydrogen storage alloy mayfurther include up to about 4 at % nickel as an equal substitute for upto about 2 at % chromium or up to about 2 at % manganese or both.Addition of nickel to the alloys can help to reduce hysteresis due toits highly catalytic nature and ductility. Nickel can also prevent theformation of body-centered cubic (BCC) secondary phase in alloys sinceits alloys have a higher averaging number of outer electrons.

To achieve non-pyrophoricity on exposure to ambient atmosphere, the at %of ductility-enhancing elements have been increased and the at % ofbrittle-enhancing elements have been decreased to reduce the inventivealloy material's decrepitation. Hydrogen embrittles metals by enteringthe grain boundaries and creating pressure at the weakest point. Thiscauses micro-cracks that begin to propagate through the grain structure.This process is known as decrepitation. Decrepitation is the main reasonfor the loss of capacity during long cycling. Usually, high contentmanganese alloys are prone to decrepitation because manganese is ahighly brittle element. Alternatively, vanadium, chromium or nickelcontaining alloys have less decrepitation issues.

Table 1 lists the compositions and properties of non-pyrophoric alloysof the present invention, two typical pyrophoric alloys and the priorart alloy of the Ovshinsky patents.

TABLE 1 Composition (at %) A/B Trapping Capacity Plateau Zr Ti V Cr MnFe Ni Al Ratio Slope Hysteresis (wt %) (wt %) (psia) HA944 5.5 27 9.320.6 31.2 5.9 0.40 0.482 0.681 0.154 0.25 1.76 55 HA1023 3.00 30.30 8.5025.00 30.00 3.00 0.20 0.499 0.799 0.087 0.25 1.74 95 HA1032 2.94 29.708.33 24.50 31.37 2.94 0.20 0.485 0.693 0.121 0.15 1.74 145 HA1036 2.9429.70 8.33 26.47 29.41 2.94 0.20 0.485 0.550 0.143 0.13 1.75 130 HA10372.94 29.70 8.33 24.50 29.41 2.94 1.98 0.20 0.485 0.642 0.042 0.18 1.73165 HA1038 3.76 28.63 8.60 25.06 29.85 3.89 0.20 0.479 0.788 0.082 0.151.73 160 HA1039 3.76 28.63 8.60 23.08 29.85 3.89 1.98 0.20 0.479 0.6930.087 0.12 1.75 140 HA1048 4.00 29.02 8.73 22.00 32.09 3.89 0.27 0.4930.511 0.262 0.15 1.74 115 Comparative pyrophoric alloys HA697 4.00 29.506.00 20.00 39.33 1.07 0.10 0.504 0.588 0.827 0.09 1.77 140 HA703 3.5029.50 8.00 20.00 37.43 1.43 0.14 0.504 0.588 0.616 0.11 1.76 135Previous invention alleys OV555 1.00 33.00 12.54 15.00 36.00 2.25 0.210.515 1.145 0.080 0.26 1.65 120 A/B ratio = A(Ti + Zr)/B(V + Cr + Mn +Fe + Al + Ni) Stope = d In P(psi)/d(Capacity(wt %)) at 20 C. Hysteresis= In Pa/In Pd at 20 C. Trapping (wt %) = trapping capacity at 14.5 psiand 20 C. Capacity (wt %) = storage capacity at 500 psi and 20 C.Plateau (psia) = desorption middle plateau pressure at 20 C.

FIG. 1 displays desorption PCT isotherm plots for examples of theinventive non-pyrophoric hydrogen storage alloys at 20° C. Samples HA697and HA703 in Table 1 and FIG. 2 are pyrophoric alloys with more thanabout 37 at % manganese. These samples are self-igniting when exposed toambient atmosphere. Alternatively, inventive alloys such as HA1036 withhigher chromium and vanadium (compared with their pyrophoriccounterparts) and less manganese are non-self-igniting.

FIG. 2 displays the absorption and desorption pressure compositiontemperature (PCT) isotherm plots of an inventive non-pyrophoric hydrogenstorage alloy (HA1036) vs. two comparable pyrophoric alloys (HA697 andHA703) at 20° C.

Another advantage of the higher content of ductility enhancing elements,such as vanadium and chromium, of the inventive hydrogen storage alloyscan increase the ductility of the metal hydride alloy, which in turn,reduces hysteresis.

To understand hysteresis, it should be noted that one of the mostimportant features of a metal hydride storage system is its plateaupressure, which indicates the pressure at which metal hydridesreversibly absorb/desorb large quantities of hydrogen. Generally, thereis a difference between equivalent pressures for absorption anddesorption in the pressure-composition isotherms. This differential inabsorption and desorption pressure is known as hysteresis.

For example, compared with the low hysteresis (0.143) HA1036, the lowvanadium and chromium HA697 and HA703 alloys have high hysteresis valuesof 0.827 and 0.616, respectively, as shown in FIG. 2 and Table 2.

TABLE 2 Composition (at %) Sample # Zr Ti V Cr Mn Fe Al Hystersis HA6974.00 29.50 6.00 20.00 39.33 1.07 0.10 0.827 HA703 3.50 29.50 8.00 20.0037.43 1.43 0.14 0.616 HA1036 2.94 29.70 8.33 26.47 29.41 2.94 0.20 0.143Hysteresis = InPa/InPd

The vanadium and manganese contents strongly affect the hysteresis ofAB₂-type Laves phase hydrogen storage alloys, while the effect of thechromium is relatively weak. High vanadium content can significantlyreduce the hysteresis, while high manganese content does the opposite.

Another reason why the inventive, high vanadium and chromium, hydrogenstorage alloys tend not to catch fire is that V and Cr tend to formdense oxide layers that can protect the alloy from further oxidation(i.e. pyrophoric burning). Alternatively, manganese and iron form porousoxide layers that cannot protect the alloy from further contacting andreacting with oxygen.

Unfortunately, a high content of vanadium and chromium in AB₂-type Lavesphase alloys tends to form a secondary body-centered cubic (BCC) phase.The BCC phase is a disordered structure of solid solution atoms andrequires elements with similar atomic sizes and low external electrons.Generally speaking, there is a body-centered cubic phase in which theaverage number of external electrons is less than 5.4. Therefore, thehigh content of titanium, vanadium and chromium in such alloys promotethe formation of the BCC phase due to their similar atomic size andlower number of external electrons.

The existence of this secondary BCC phase distorts the flatness of theplateau pressure of the PCT isotherms because the BCC phase has twohydride structures. These include a BCC phase where hydrogen atomsoccupy octahedral sites and a face-centered cubic (FCC) phase wherehydrogen atoms are located in tetrahedral sites. Usually, the hydrogenin large octahedral sites of the BCC hydride phase is irreversible,thereby trapping a huge amount of hydrogen, while the hydrogen in thesmall tetrahedral sites of the FCC phase is reversible, but plateaupressures of the FCC phase may not be the range of AB₂-type Laves phasealloys.

Since manganese has a larger atomic radius and a high number of externalelectrons, a high content of manganese can prevent the formation of asecond BCC phase in the AB₂-type Laves phase. Therefore, thehigh-content manganese AB₂-type alloy has a relatively flat plateaupressure but has a high degree of self-ignitability and high hysteresis.In order to achieve non-ignition and low hysteresis, the manganesecontent in AB₂ alloy should not exceed about 33 at %. More preferablythe manganese does not exceed about 32 at %.

Adding zirconium to the alloys can help to reduce the formation of thesecondary BCC phase. This is because zirconium atoms are large and donot like to form disordered solid solution phases with titanium,vanadium and chromium. The addition of Zr to AB₂ alloys can result inhydrogen storage alloys having high thermal stability and low plateaupressures. This is because of zirconium's large radius and lowelectronegativity.

FIG. 3 displays desorption PCT isotherm plots exhibiting the effects ofzirconium contents on the plateau pressures of the inventivenon-pyrophoric hydrogen storage alloys at 20° C. This is evidenced bythe difference in plateau pressure of alloys with differing Zr content.The middle plateau pressure of HA944 (with 5.5 at % Zr) is 55 psia whilethose of HA1040 (with 3.78 at % Zr) and HA1032 (with 2.94 at % Zr) are110 psia and 145 psia, respectively (See Table 1).

For AB₂-type Laves phase alloys, the Zr/Ti ratio controls thetetrahedral interstitial sites and average electronegativity, as well asdetermining plateau pressures. Lower Zr/Ti values facilitate theformation of alloys with high plateau pressures while higher valuesresult in lower plateau pressures. Thus, the plateau pressure can be, atleast somewhat, tailored to the needs of the end use of the hydrogenstorage alloys.

In AB₂-type Laves phase, the A/B ratio can affect plateau flatness. TheA/B ratio has been slightly reduced to less than or equal to 0.5 tolimit formation of any secondary BCC phase. This is because A-siteelements, which have low outer electron numbers, favor the formation ofthe BCC disordered solid solution phase. Therefore, alloys that are leanin A-site elements limit the secondary phase. The existence of thesecondary BCC phase can destroy the flatness of the plateau because theBCC phase has two hydride structures, that is, the BCC phase wherehydrogen atoms occupy octahedral sites and the FCC phase where hydrogenatoms are located at tetrahedral sites. The hydrogen stored at theoctahedral sites of the BCC hydride phase is irreversible at reasonablepressures and temperatures, thus forming hydrogen traps in the metallattice. Although the hydrogen at tetrahedral sites of the FCC phase isreversible, the plateau pressures are not as useful as those in theAB₂-type Laves phase.

FIG. 4 displays desorption PCT isotherm plots (at 20° C.) of the A-sitelean inventive alloy HA1032 vs. the A-site rich prior art alloy OV555.The alloy OV555 with an A/B ratio of 0.515 exhibits a high slope of1.145 and a high trapping of 0.26 wt %, while the alloy of the presentinvention HA1032 with an A/B ratio of 0.485 exhibits a low slope of0.693 and a low trapping of 0.15 wt %. This indicates that the A/B ratiosignificantly affects plateau pressures and plateau flatness. Thus,reduction of the A/B ratio has led to the formation of alloys with highplateau pressures as well as flatter plateaus.

While decrepitation is the main reason for the loss of capacity duringlong cycling and pyrophoric burning, another reason is partly related tothe stresses and strains of charging/discharging cycling. Highhysteresis usually exhibits high stresses and strains, thereby resultingin high decrepitation. Some elements, such as vanadium, chromium andnickel, could reduce this disadvantage in such materials.

The price of pure vanadium is several times higher than ferrovanadium.Replacement of pure vanadium with low-cost ferrovanadium willsignificantly reduce cost of materials to produce the alloys. Typically,ferrovanadium alloy contains 15%-17% Fe and 1%-2% Al. Iron negativelyaffects the flammability and high hysteresis of AB₂-type Laves phasealloys, while aluminum negatively affects capacity and platformflatness, resulting in lower levels of both elements and betterperformance. Table 3 lists the compositions and properties ofnon-pyrophoric alloys with low Fe contents of the present invention.FIG. 5 displays desorption PCT isotherm plots for examples of theinventive non-pyrophoric hydrogen storage alloys with low Fe contents at20° C.

TABLE 3 Composition (at %) A/B Trapping Capacity Plateau Zr Ti V Cr MnFe Ni Al Ratio Slope Hysteresis (wt %) (wt %) (psia) HA1068 3.70 29.108.40 24.10 31.03 1.52 2.00 0.15 0.488 0.667 0.092 0.10 1.78 152 HA10723.50 29.10 8.40 24.20 31.13 1.52 2.00 0.15 0.484 0.697 0.108 0.09 1.77157 HA1075 3.50 29.10 8.40 25.33 32.00 1.52 0.15 0.484 0.702 0.185 0.101.77 166 HA1077 3.50 29.10 8.40 24.20 30.13 1.52 3.00 0.15 0.484 0.5040.131 0.09 1.78 150 HA1079 3.50 28.80 8.40 24.30 29.33 1.52 4.00 0.150.477 0.486 0.101 0.10 1.78 195 HA1087 4.00 28.80 8.40 25.00 30.13 1.522.00 0.15 0.488 0.631 0.181 0.09 1.78 112 HA1092 3.00 29.50 8.40 26.0029.43 1.52 2.00 0.15 0.481 0.707 0.106 0.08 1.77 215 A/B ratio = A(Ti +Zr)/B(V + Cr + Mn + Fe + Al + Ni) Slope = d In P(psi)/d(Capacity(wt %))at 20 C. Hysteresis = In Pa/In Pd at 20 C. Trapping (wt %) = trappingcapacity at 14.5 psi and 20 C. Capacity (wt %) = storage capacity at 500psi and 20 C. Plateau (psia) = desorption middle plateau pressure at 20C.

The Zr can be about 2.0 at %, 2.1 at %, 2.2 at %, 2.3 at %, 2.4 at %,2.5 at %, 2.6 at %, 2.7 at %, 2.8 at %, 2.9 at %, 3.0 at %, 3.1 at %,3.2 at %, 3.3 at %, 3.4 at %, 3.5 at %, 3.6 at %, 3.7 at %, 3.8 at %,3.9 at %, 4.0 at %, 4.1 at %, 4.2 at %, 4.3 at %, 4.4 at %, 4.5 at %,4.6 at %, 4.7 at %, 4.8 at %, 4.9 at %, 5.0 at %, 5.1 at %, 5.2 at %,5.3 at %, 5.4 at %, 5.5 at % or other incremental at % between.

The Ti can be about 27.0 at %, 27.1 at %, 27.2 at %, 27.3 at %, 27.4 at%, 27.5 at %, 27.6 at %, 27.7 at %, 27.8 at %, 27.9 at %, 28.0 at %,28.1 at %, 28.2 at %, 28.3 at %, 28.4 at %, 28.5 at %, 28.6 at %, 28.7at %, 28.8 at %, 28.9 at %, 29.0 at %, 29.1 at %, 29.2 at %, 29.3 at %,29.4 at %, 29.5 at %, 29.6 at %, 29.7 at %, 29.8 at %, 29.9 at %, 30.0at %, 30.1 at %, 30.2 at %, 30.3 at %, 30.4 at %, 30.5 at %, 30.6 at %,30.7 at %, 30.8 at %, 30.9 at %, 31.0 at %, 31.1 at %, 31.2 at %, 3.3 at% or other incremental at % between.

The V can be about 8.3 at %, 8.4 at %, 8.5 at %, 8.6 at %, 8.7 at %, 8.8at %, 8.9 at %, 9.0 at %, 9.1 at %, 9.2 at %, 9.3 at %, 9.4 at %, 9.5 at%, 9.6 at %, 9.7 at %, 9.8 at %, 9.9 at % or other incremental at %between.

The Cr can be about 20.6 at %, 20.7 at %, 20.8 at %, 20.9 at %, 21.0 at%, 21.1 at %, 21.2 at %, 21.3 at %, 21.4 at %, 21.5 at %, 21.6 at %,21.7 at %, 21.8 at %, 21.9 at %, 22.0 at %, 22.1 at %, 22.2 at %, 22.3at %, 22.4 at %, 22.5 at %, 22.6 at %, 22.7 at %, 22.8 at %, 22.9 at %,23.0 at %, 23.1 at %, 23.2 at %, 23.3 at %, 23.4 at %, 23.5 at %, 23.6at %, 23.7 at %, 23.8 at %, 23.9 at %, 24.0 at %, 24.1 at %, 24.2 at %,24.3 at %, 24.4 at %, 24.5 at %, 24.6 at %, 24.7 at %, 24.8 at %, 24.9at %, 25.0 at %, 25.1 at %, 25.2 at %, 25.3 at %, 25.4 at %, 25.5 at %,25.6 at %, 25.7 at %, 25.8 at %, 25.9 at %, 26.0 at %, 26.1 at %, 26.2at %, 26.3 at %, 26.4 at %, 26.5 at %, 26.6 at %, 26.7 at %, 26.8 at %,26.9 at %, 27.0 at %, 27.1 at %, 27.2 at %, 27.3 at %, 27.4 at %, 27.5at %, 27.6 at %, 27.7 at %, 27.8 at %, 27.9 at %, 28.0 at %, 28.1 at %,28.2 at %, 28.3 at %, 28.4 at %, 28.5 at %, 28.6 at %, 28.7 at %, 28.8at %, 28.9 at %, 29.0 at %, 29.1 at %, 29.2 at %, 29.3 at %, 29.4 at %,29.5 at %, 29.6 at %, 29.7 at %, 29.8 at %, 29.9 at %, 30.0 at %, 30.1at %, 30.2 at %, 30.3 at %, 30.4 at %, 30.5 at % or other incremental at% between.

The Mn can be about 25.4 at %, 25.5 at %, 25.6 at %, 25.7 at %, 25.8 at%, 25.9 at %, 26.0 at %, 26.1 at %, 26.2 at %, 26.3 at %, 26.4 at %,26.5 at %, 26.6 at %, 26.7 at %, 26.8 at %, 26.9 at %, 27.0 at %, 27.1at %, 27.2 at %, 27.3 at %, 27.4 at %, 27.5 at %, 27.6 at %, 27.7 at %,27.8 at %, 27.9 at %, 28.0 at %, 28.1 at %, 28.2 at %, 28.3 at %, 28.4at %, 28.5 at %, 28.6 at %, 28.7 at %, 28.8 at %, 28.9 at %, 29.0 at %,29.1 at %, 29.2 at %, 29.3 at %, 29.4 at %, 29.5 at %, 29.6 at %, 29.7at %, 29.8 at %, 29.9 at %, 30.0 at %, 30.1 at %, 30.2 at %, 30.3 at %,30.4 at %, 30.5 at %, 30.6 at %, 30.7 at %, 30.8 at %, 30.9 at %, 31.0at %, 31.1 at %, 31.2 at %, 31.3 at %, 31.4 at %, 31.5 at %, 31.6 at %,31.7 at %, 31.8 at %, 31.9 at %, 32.0 at %, 32.1 at %, 32.2 at %, 32.3at %, 32.4 at %, 32.5 at %, 32.6 at %, 32.7 at %, 32.8 at %, 32.9 at %,33.0 at % or other incremental at % between.

The Fe can be about 1.0 at %, 1.1 at %, 1.2 at %, 1.3 at %, 1.4 at %,1.5 at %, 1.6 at %, 1.7 at %, 1.8 at %, 1.9 at %, 2.0 at %, 2.1 at %,2.2 at %, 2.3 at %, 2.4 at %, 2.5 at %, 2.6 at %, 2.7 at %, 2.8 at %,2.9 at %, 3.0 at %, 3.1 at %, 3.2 at %, 3.3 at %, 3.4 at %, 3.5 at %,3.6 at %, 3.7 at %, 3.8 at %, 3.9 at %, 4.0 at %, 4.1 at %, 4.2 at %,4.3 at %, 4.4 at %, 4.5 at %, 4.6 at %, 4.7 at %, 4.8 at %, 4.9 at %,5.0 at %, 5.1 at %, 5.2 at %, 5.3 at %, 5.4 at %, 5.5 at %, 5.6 at %,5.7 at %, 5.8 at %, 5.9 at % or other incremental at % between.

The Al can be about 0.1 at %, 0.2 at %, 0.3 at %, 0.4 at % or otherincremental percentage between.

The Ni can be about 0.0 at %, 0.1 at %, 0.2 at %, 0.3 at %, 0.4 at %,0.5 at %, 0.6 at %, 0.7 at %, 0.8 at %, 0.9 at %, 1.0 at %, 1.1 at %,1.2 at %, 1.3 at %, 1.4 at %, 1.5 at %, 1.6 at %, 1.7 at %, 1.8 at %,1.9 at %, 2.0 at %, 2.1 at %, 2.2 at %, 2.3 at %, 2.4 at %, 2.5 at %,2.6 at %, 2.7 at %, 2.8 at %, 2.9 at %, 3.0 at %, 3.1 at %, 3.2 at %,3.3 at %, 3.4 at %, 3.5 at %, 3.6 at %, 3.7 at %, 3.8 at %, 3.9 at %,4.0 at % or other incremental at % between.

The Ba, Co, Cu, Cs, K, Li, Mm, Mo, Na, Nb, Ni, Rb, Ta, Tl, and W (whereMm is mischmetal) can be about 1.0 at %, 1.1 at %, 1.2 at %, 1.3 at %,1.4 at %, 1.5 at %, 1.6 at %, 1.7 at %, 1.8 at %, 1.9 at %, 2.0 at %,2.1 at %, 2.2 at %, 2.3 at %, 2.4 at %, 2.5 at %, 2.6 at %, 2.7 at %,2.8 at %, 2.9 at %, 3.0 at %, 3.1 at %, 3.2 at %, 3.3 at %, 3.4 at %,3.5 at %, 3.6 at %, 3.7 at %, 3.8 at %, 3.9 at %, 4.0 at %, 4.1 at %,4.2 at %, 4.3 at %, 4.4 at %, 4.5 at %, 4.6 at %, 4.7 at %, 4.8 at %,4.9 at %, 5.0 at %, 5.1 at %, 5.2 at %, 5.3 at %, 5.4 at %, 5.5 at %,5.6 at %, 5.7 at %, 5.8 at %, 5.9 at %, 6.0 at %, 6.1 at %, 6.2 at %,6.3 at %, 6.4 at %, 6.5 at %, 6.6 at %, 6.7 at %, 6.8 at %, 6.9 at %,7.0 at %, 7.1 at %, 7.2 at %, 7.3 at %, 7.4 at %, 7.5 at %, 7.6 at %,7.7 at %, 7.8 at %, 7.9 at %, 8.0 at %, 8.1 at %, 8.2 at %, 8.3 at %,8.4 at %, 8.5 at %, 8.6 at %, 8.7 at %, 8.8 at %, 8.9 at %, 9.0 at %,9.1 at %, 9.2 at %, 9.3 at %, 9.4 at %, 9.5 at %, 9.6 at %, 9.7 at %,9.8 at %, 9.9 at %, 10.0 at % or other incremental at % between.

The alloy can have a trapped hydrogen capacity (at about 14.5 psi andabout 20° C.) of no more than about 0.08 wt %, 0.09 wt %, 0.10 wt %,0.11 wt %, 0.12 wt %, 0.13 wt %, 0.14 wt %, 0.15 wt %, 0.16 wt %, 0.17wt %, 0.18 wt %, 0.19 wt %, 0.20 wt %, 0.21 wt %, 0.22 wt %, 0.23 wt %,0.24 wt %, 0.25 wt % other incremental wt % between. The alloy can havea trapped hydrogen capacity (at about 14.5 psi and about 20° C.) of lessthan 0.08 wt %.

The alloy can have a PCT isotherm slope of no more than about 0.50,0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62,0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74,0.75, 0.76, 0.77, 0.78, 0.79, 0.80 or other incremental value between.The alloy can have a PCT isotherm slope of less than 0.50.

The alloy can have a hysteresis of not more than about 0.04, 0.05, 0.06,0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18,0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30,0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42,0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50 or other incrementalvalue between.

The alloy can have a total hydrogen storage capacity (at about 500 psiand about 20° C.) of at least about 1.70 wt %, 1.71 wt %, 1.72 wt %,1.73 wt %, 1.74 wt %, 1.75 wt %, 1.76 wt %, 1.77 wt %, 1.78 wt %, 1.79wt %, 1.80 wt % other incremental wt % between. The alloy can have atotal hydrogen storage capacity (at about 500 psi and about 20° C.) ofgreater than 1.80 wt %.

The hydrogen storage system 1 of the present invention can be seen inFIG. 6 . FIG. 6 depicts the hydrogen storage system 1 which includes ahydrogen storage alloy containment vessel. The hydrogen storage alloycontainment vessel includes an external pressure containment vessel 2.The hydrogen storage alloy containment vessel further includes athermally conductive compartmentalization network 3 disposed within theexternal pressure containment vessel 2. The thermally conductivecompartmentalization network 3 creates thermally conductive compartmentswithin the external pressure containment vessel 2. A hydrogen storagealloy 7 is disposed within the thermally conductive compartments of thethermally conductive compartmentalization network 3. Typically, aconventional pressure valve 4 is connected to the valve opening of theexternal pressure containment vessel 2 to control inflow and outflow ofhydrogen gas from the external pressure containment vessel 2 for storagein the hydrogen storage alloy 7. Other embodiments many includedifferent or specialized pressure valves that interface with othersystems, such as other types of storage systems, vehicles, engines,equipment or any other system that uses hydrogen whether known orunknown.

FIG. 7 depicts a magnified image of the top of the hydrogen storagesystem 1. As depicted in FIG. 7 , the thermally conductivecompartmentalization network 3 is formed from a plurality of elongatetubes 5, which are positioned within the external pressure containmentvessel 2. The plurality of elongate tubes 5 are packed into the externalpressure containment vessel 2 to form a coherent, tightly packed bundle,wherein longitudinal axes of the elongate tubes 5 are parallel to alongitudinal axis of the external pressure containment vessel 2. Theelongate tubes 5 are preferably thin walled and made of aluminum,copper, magnesium or alloys of these metals to avoid any problem withinteraction between the elongate tubes and the hydrogen atmospherewithin the external pressure containment vessel 2. The external pressurecontainment vessel 2 can be made of aluminum, copper, stainless steel,carbon steel, and other metals when properly designed in accordance withknown technology.

The elongate tubes 2 are packed firmly into a bundle within the externalpressure containment vessel 2 so that each elongate tube 5 in the bundleis in firm contact along its longitudinal surface with the longitudinalsurfaces of other elongate tubes 5. In addition, the outer elongatetubes 5 in the bundle make firm contact along their longitudinalsurfaces with the longitudinal inside surface of the external pressurecontainment vessel 2.

The otherwise void spaces remaining in the external pressure containmentvessel 2 containing the elongate tubes 5 are substantially filled with aparticulate, hydrogen storage alloy 7 (see FIGS. 8A-8B). FIGS. 7A and 7Breflect designs of the elongate tube size, wherein the elongate tubes 5of FIG. 8A all have the same outer diameter, and the elongate tubes 5 ofFIG. 8B have variable outer diameter.

To facilitate filling of the otherwise void spaces with hydrogen storagealloy 7, a plurality of spaced apart notches 6 (see FIG. 7 ) areprovided in the longitudinal sides of each of the elongate tubes 5. Thenotches 6 are arranged randomly around each tube to provide one or moreaccess openings to the interior of each elongate tube 5. The notches 6allow particulate hydrogen storage alloy 7 to flow to and from theinterior of the elongate tubes 5 and the spaces between elongate tubes,thereby facilitating the filling of the void spaces with the hydrogenstorage alloy 7.

The elongate tubes 5 can be positioned within the external pressurecontainment vessel 2 during the manufacture of the external pressurecontainment vessel 2, or, as will be further explained hereinafter, theelongate tubes 5 can be retrofitted in an existing external pressurecontainment vessel 2. If positioned in the external pressure containmentvessel 2 during the construction of the external pressure containmentvessel 2, the elongate tubes 5 are inserted through the open end of theproto-vessel prior to the rolling down of that end to form the valveopening therein. This entails having the full bundle of elongate tubes 5in the external pressure containment vessel 2 during the rolling andforming of the valve opening.

It is advantageous to retrofit the elongate tubes 5 into a completelyformed pressure vessel, thus avoiding interposing the step of insertingthe elongate tubes 5 into the external pressure containment vessel 2during the manufacturing thereof. The elongate tubes 5 are readilyinserted into the external pressure containment vessel 2 through thevalve opening. The elongate tubes 5 are cut to lengths having alongitudinal dimension shorter than the longitudinal dimension of theexternal pressure containment vessel 2. The lengths of elongate tube 5are then inserted one at a time into the external pressure containmentvessel 2 through the valve opening therein. The elongate tubes 5 areorganized into a tightly packed tube bundle as best illustrated in FIG.7 . Adjacent elongate tubes 5 are in firm contact along the longitudinalsides thereof, and the outer elongate tubes 5 of the bundle also makefirm contact along their longitudinal surfaces with the longitudinal,inside surface of the external pressure containment vessel 2.

Following installation of the elongate tubes 5 into the externalpressure containment vessel 2, the hydrogen storage alloy 7 isintroduced into the vessel 11 through the valve opening. Sufficienthydrogen storage alloy 7 is added to the external pressure containmentvessel 2 to substantially fill the otherwise void volume within theelongate tubes 5 and the spaces between adjacent elongate tubes 5.

While the elongate tubes 5 may be cylindrical elongate tubes, they mayalso have non-cylindrical shapes. FIGS. 9A and 9B depict cross-sectionsof non-cylindrically shaped elongate tubes 5′ that may be useful in thehydrogen storage system of the present invention. FIG. 9A depicts thecross-section of a three-sided elongate tube 5′, while FIG. 9B depictsthe cross-section of a four-sided elongate tube 5′. Such non-cylindricalelongate tubes 5′ may be used in conjunction with the cylindricalelongate tubes 5 to increase the packing density of the tubes within theexternal pressure containment vessel 2. This in turn leads to higherthermal conductivity of the thermally conductive compartmentalizationnetwork 3 and thermal connection to the external pressure containmentvessel 2.

Also, while the elongate tubes 5 may be smooth-walled elongate tubes,they may also have non-smooth-walled shapes. FIGS. 9C and 9D depictcross-sections of non-smooth-walled shaped elongate tubes 5″ that may beuseful in the hydrogen storage system of the present invention. FIG. 9Cdepicts the cross-section of an elongate tube 5″ having a smooth-walledinner surface and a corrugated exterior wall. FIG. 9D depicts thecross-section of an elongate tube 5″ having corrugated interior andexterior walls. Such non-smooth-walled elongate tubes 5″ may aid inincreasing the thermal contact area between the individual elongatetubes within the thermally conductive compartmentalization network 3,but also increasing the thermal surface contact area between thehydrogen storage alloy 7 and the tubes of the thermally conductivecompartmentalization network 3. It should also be noted that thenon-cylindrically shaped elongate tubes 5′ may also havecorrugated-walled surfaces.

Alternatively, the entire hydrogen storage system 1, including theexternal pressure containment vessel 2 and the thermally conductivecompartmentalization network 3, can be formed simultaneously via 3Dprinting technology. This usually includes methods of 3D printing ofmetal.

Metal 3D printing is a catchall term for several technology families.Simply put, metal 3D printing refers to any technology that createsmetal objects layer by layer through sintering, melting, and weldingwith metal.

Metal 3D printing is one of the most heavily invested in andfastest-growing manufacturing technologies. It can be used inconjunction with other manufacturing technologies, but it is alsocapable of producing prototypes and finished products on its own. Insome cases, 3D-printed metal objects perform just as well as machinedparts. It can be in prototyping, aerospace, mechanical engineering,specific tools, and other applications.

Aluminum is a lightweight alloy with high flexibility, good strength,and superior thermal properties and it has become the primary metal usedin 3D printing. Aluminum 3D printers have been used in biomedical,automotive, and aerospace applications. Aluminum's core strength is itsability to be molded and used for functional objects as well asprototypes. The material is suitable for both prototyping andmanufacturing. The quality of 3D-printed aluminum parts is comparable tothat of synthetic parts. Aluminum's material properties make it anexcellent choice for high-performance functional parts that aresubjected to high loads.

Available 3D printing technologies include, but are not limited to:

-   -   1. Fused Deposition Modeling (FDM)    -   2. Stereolithography (SLA)    -   3. Digital Light Processing (DLP)    -   4. Selective Laser Sintering (SLS)    -   5. Material Jetting (MJ)    -   6. Drop on Demand (DoD)    -   7. Sand Binder Jetting    -   8. Metal Binder Jetting    -   9. Direct Metal Laser Sintering (DMLS) and Selective Laser        Melting (SLM); and    -   10. Electron Beam Melting (EBM).

Of these, DMSL/SLM can be considered a useful technique for forming theentire hydrogen storage system 1.

Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS)are two metal additive manufacturing processes that use metal powder bedfusion, the process where a heat source is utilized to fuse metalparticles one layer at a time. Both make objects in a way similar toSLS, the main difference being these technologies are used in theproduction of metal parts instead of plastic. Typical materials used aremetal powder, aluminum, stainless steel, and titanium.

DMLS is used for producing parts from metal alloys. Instead of meltingit, DMLS heats the metal powder with a laser to the point where it fusestogether on a molecular level. SLM uses the laser to fully melt themetal powder to form a homogeneous part, in other words, it makes partsfrom single element materials, such as titanium.

DMLS and SLM processes do need structural support in order to limit thepossibility of distortion, which can result from the high temperaturesused during printing. The two technologies have a lot of similarities:both use a laser to scan and selectively fuse (or melt) metal powderparticles, bonding them together and building a part layer-by-layer.Also, the materials used in both processes are metals that come in agranular/powder form.

The differences between SLM and DMLS come down to the fundamentals ofthe particle bonding process. SLM uses metal powders with a singlemelting temperature and fully melts the particles, while in DMLS thepowder is composed of materials with variable melting points that fuseon a molecular level at elevated temperatures. Essentially, SLM producesparts from a single metal, while DMLS produces parts from metal alloys.

Both SLM and DMLS are used in industrial applications to create end-useengineering products. Using such technologies, the entire hydrogenstorage system 1, including the external pressure containment vessel 2and the thermally conductive compartmentalization network 3 can beformed simultaneously.

Accordingly a method of fabricating the hydrogen storage system mayinclude fabricating the external pressure containment vessel and thethermally conductive compartmentalization network disposed within theexternal pressure containment vessel via 3D metal printing, anddepositing the hydrogen storage alloy within the hydrogen storage alloycontainment vessel. The external pressure containment vessel and saidthermally conductive compartmentalization network disposed within saidexternal pressure containment vessel may be formed simultaneously via 3Dmetal printing, such as 3D printing of aluminum and/or aluminum alloys.The 3D metal printing of aluminum and/or aluminum alloys may includedeposition by Selective Laser Melting (SLM) and/or Direct Metal LaserSintering (DMLS).

It will be understood that particular embodiments described herein areshown by way of illustration and not as limitations of the invention.The principal features of this invention can be employed in variousembodiments without departing from the scope of the invention. Thoseskilled in the art will recognize, or be able to ascertain using no morethan routine experimentation, numerous equivalents to the specificprocedures described herein. Such equivalents are considered to bewithin the scope of this invention and are covered by the claims.

All publications, patent applications and patents mentioned in thespecification are indicative of the level of skill of those skilled inthe art to which this invention pertains. All publications and patentapplications are herein incorporated by reference to the same extent asif each individual publication or patent application was specificallyand individually indicated to be incorporated by reference.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more,” “at least one,”and “one or more than one.” The use of the term “or” in the claims isused to mean “and/or” unless explicitly indicated to refer toalternatives only or the alternatives are mutually exclusive, althoughthe disclosure supports a definition that refers to only alternativesand “and/or.” Throughout this application, the term “about” is used toindicate that a value includes the inherent variation of error for thedevice, the method being employed to determine the value, or thevariation that exists among the study subjects.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “includes” and “include”) or “containing”(and any form of containing, such as “contains” and “contain”) areinclusive or open-ended and do not exclude additional, unrecitedelements or method steps. In embodiments of any of the compositions andmethods provided herein, “comprising” may be replaced with “consistingessentially of” or “consisting of”. As used herein, the phrase“consisting essentially of” requires the specified integer(s) or stepsas well as those that do not materially affect the character or functionof the claimed invention. As used herein, the term “consisting” is usedto indicate the presence of the recited integer (e.g., a feature, anelement, a characteristic, a property, a method/process step or alimitation) or group of integers (e.g., feature(s), element(s),characteristic(s), propertie(s), method/process steps or limitation(s))only.

The term “or combinations thereof” as used herein refers to allpermutations and combinations of the listed items preceding the term.For example, “A, B, C, or combinations thereof” is intended to includeat least one of: A, B, C, AB, AC, BC, or ABC, and if order is importantin a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB.Continuing with this example, expressly included are combinations thatcontain repeats of one or more item or term, such as BB, AAA, AB, BBC,AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan willunderstand that typically there is no limit on the number of items orterms in any combination, unless otherwise apparent from the context.

As used herein, words of approximation such as, without limitation,“about”, “substantial” or “substantially” refers to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skilled in the art recognizethe modified feature as still having the required characteristics andcapabilities of the unmodified feature. In general, but subject to thepreceding discussion, a numerical value herein that is modified by aword of approximation such as “about” may vary from the stated value byat least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

All of the devices and/or methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the devices and/or methods of this invention have beendescribed in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and/or methods and in the steps or in the sequence of stepsof the method described herein without departing from the concept,spirit and scope of the invention. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope and concept of the invention as defined by theappended claims.

Furthermore, no limitations are intended to the details of constructionor design herein shown, other than as described in the claims below. Itis therefore evident that the particular embodiments disclosed above maybe altered or modified and all such variations are considered within thescope and spirit of the disclosure. Accordingly, the protection soughtherein is as set forth in the claims below.

To aid the Patent Office, and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims to invokeparagraph 6 of 35 U.S.C. § 112 as it exists on the date of filing hereofunless the words “means for” or “step for” are explicitly used in theparticular claim.

What is claimed is:
 1. A hydrogen storage system comprising: a hydrogenstorage alloy containment vessel, wherein said hydrogen storage alloycontainment vessel comprises: an external pressure containment vessel; athermally conductive compartmentalization network disposed within saidexternal pressure containment vessel, said thermally conductivecompartmentalization network creating compartments within said pressurevessel within which a hydrogen storage alloy is disposed; wherein saidthermally conductive compartmentalization network includes a pluralityof elongate tubes being made of a thermally conductive metal or alloyselected from the group consisting of aluminum, magnesium, copper andalloys of these metals, and being positioned within said externalpressure containment vessel with longitudinal axes of said elongatetubes being parallel to the longitudinal axis of said external pressurecontainment vessel, said plurality of elongate tubes forming a coherent,tightly packed tube bundle within said external pressure containmentvessel such that said coherent, tightly packed bundle provides athermally conductive network between said hydrogen storage alloy andsaid external pressure containment vessel; said hydrogen storage alloydisposed within said hydrogen storage alloy containment vessel, whereinsaid hydrogen storage alloy comprises a non-pyrophoric AB₂ Laves phasehydrogen storage alloy comprising: an A-site to B-site elemental ratioof not more than about 0.5; and an alloy composition including about (inat %): Zr: 2.0-5.5, Ti: 27-31.3, V: 8.3-9.9, Cr: 20.6-30.5, Mn:25.4-33.0, Fe: 1.0-5.9, and Al: 0.1-0.4.
 2. The hydrogen storage systemof claim 1, wherein said alloy composition includes (in at %): Zr:2.9-5.5, Ti: 27-30.3, V: 8.3-9.3, Cr: 20.6-26.5, Mn: 29.4-32.1, Fe:1.5-5.9, and Al: 0.1-0.4.
 3. The hydrogen storage system of claim 1,wherein said alloy composition further includes up to about 4 at %nickel as an equal substitute for up to about 2 at % chromium or up toabout 2 at % manganese or both.
 4. The hydrogen storage system of claim1, wherein said alloy has a total hydrogen storage capacity of at leastabout 1.7 wt % at about 500 psi and about 20° C.
 5. The hydrogen storagesystem of claim 1, wherein said alloy has a total hydrogen storagecapacity of at least about 1.8 wt % at about 500 psi and about 20° C. 6.The hydrogen storage system of claim 1, wherein said alloy has a trappedhydrogen capacity of no more than about 0.25 wt % at about 14.5 psi andabout 20° C.
 7. The hydrogen storage system of claim 1, wherein saidalloy has a trapped hydrogen capacity of no more than about 0.20 wt % atabout 14.5 psi and about 20° C.
 8. The hydrogen storage system of claim1, wherein said alloy has a trapped hydrogen capacity of no more thanabout 0.15 wt % at about 14.5 psi and about 20° C.
 9. The hydrogenstorage system of claim 1, wherein said alloy has a trapped hydrogencapacity of no more than about 0.10 wt % at about 14.5 psi and about 20°C.
 10. The hydrogen storage system of claim 1, wherein said alloy has apressure composition temperature (PCT) isotherm slope of no more thanabout 0.8.
 11. The hydrogen storage system of claim 1, wherein saidalloy has a PCT isotherm slope of no more than about 0.7.
 12. Thehydrogen storage system of claim 1, wherein said alloy has a PCTisotherm slope of no more than about 0.6.
 13. The hydrogen storagesystem of claim 1, wherein said alloy has a hysteresis of not more thanabout 0.5.
 14. The hydrogen storage system of claim 1, wherein saidalloy has a hysteresis of not more than about 0.4.
 15. The hydrogenstorage system of claim 1, wherein said alloy has a hysteresis of notmore than about 0.3.
 16. The hydrogen storage system of claim 1, whereinsaid alloy has a hysteresis of not more than about 0.2.
 17. The hydrogenstorage system of claim 1, wherein said alloy has a hysteresis of notmore than about 0.1.
 18. The hydrogen storage system of claim 1, whereinin the alloy composition further comprises about 1.0-10.0 at % total ofat least one element selected from the group consisting of Ba, Co, Cu,Cs, K, Li, Mm, Mo, Na, Nb, Ni, Rb, Ta, Tl, and W (where Mm ismischmetal).
 19. The hydrogen storage system of claim 1, wherein anouter diameter of all tubes of said plurality of elongate tubes is thesame.
 20. The hydrogen storage system of claim 1, wherein an outerdiameter of each tube of said plurality of elongate tubes is variable.21. The hydrogen storage system of claim 1, wherein at least some tubesof said plurality of elongate tubes have one or more notches provided inlongitudinal sides thereof providing access openings to an interior ofsaid tubes.
 22. The hydrogen storage system of claim 1, wherein at leastsome tubes of said plurality of elongate tubes have a non-cylindricalcross-section.
 23. The hydrogen storage system of claim 1, wherein atleast some tubes of said plurality of elongate tubes have a corrugatedinterior and/or exterior wall surfaces.
 24. The hydrogen storage systemof claim 1, further comprising a pressure valve connected to a valveopening of the external pressure containment vessel.
 25. The hydrogenstorage system of claim 1, wherein said external pressure containmentvessel and said thermally conductive compartmentalization networkdisposed within said external pressure containment vessel are formedsimultaneously via 3D metal printing.
 26. The hydrogen storage system ofclaim 25, wherein said 3D metal printing comprises 3D printing ofaluminum and/or aluminum alloys.
 27. The hydrogen storage system ofclaim 26, wherein said 3D metal printing of aluminum and/or aluminumalloys comprises deposition by Selective Laser Melting (SLM) and/orDirect Metal Laser Sintering (DMLS).
 28. A method of fabricating saidhydrogen storage system of claim 1, comprising: fabricating saidexternal pressure containment vessel and said thermally conductivecompartmentalization network disposed within said external pressurecontainment vessel via 3D metal printing; and depositing said hydrogenstorage alloy within said hydrogen storage alloy containment vessel. 29.The method of claim 28, wherein said external pressure containmentvessel and said thermally conductive compartmentalization networkdisposed within said external pressure containment vessel are formedsimultaneously via said 3D metal printing.
 30. The method of claim 28,wherein said 3D metal printing comprises 3D printing of aluminum and/oraluminum alloys.
 31. The method of claim 30, wherein said 3D metalprinting of aluminum and/or aluminum alloys comprises deposition bySelective Laser Melting (SLM) and/or Direct Metal Laser Sintering(DMLS).